The present invention relates to hydraulic control systems and pertains particularly to a digital positioner for a remote hydraulic control valve.
It is frequently desirable to operate a hydraulic machine from a remote location. Such a remote location may be desirable, for example, in mining operations wherein the dangers of caving or the like presents a hazard to the machine operator. Other environments may also present hazardous conditions to the operator of the vehicle.
Considerable control for remote operation may also permit an operator to operate a plurality of machines in tandem. Such remote operation of machines is not too difficult where the valves for the hydraulic system are either fully open or fully closed. Such operation does, however, become a problem when it is desirable to operate a system with the control valves at intermediate positions between full open and full closed.
Remote control of a movable machine is difficult to achieve by hydraulic control means from a remote location. Such remote control is usually achieved by radio control or by electrical conductor cables or the like. With such an arrangement, the electrical control may either control a main valve or a pilot control system. A difficulty with such electrical control is that intermediate stops between full open and full closed is not easily achievable by low cost electrical control.
Furthermore, it will also be appreciated that certain hydraulically controlled machines have implement functions remote from the operator requiring pilot systems. Also, high horsepower hydraulic systems require pilot systems to overcome high actuating forces. Electrical control systems replace pilot lines with electrical lines that are more economical, less cumbersome and leak free. Electrical control offers remote control between the operator on the vehicle and the implement valve.
It will also be appreciated that certain hydraulically controlled machines have implements that perform functions in sequence. For example, such machines have a tool or implement that performs one function and immediately thereafter performs a second related function. These functions are normally performed in specified sequence.
Hydraulic loaders are examples of machines having such a function. For example, a loaded bucket is raised to a given height and following this raise to that height the bucket is dumped. Thereafter, the bucket is lowered to ground level and, after being moved forward for loading, is then racked back, that is, tilted back to reduce spillage as the load is raised for dumping into a vehicle or the like. It will be appreciated that numerous other machines having examples of such sequence operation exist.
These sequence functions can be controlled by a single control valve being movable to a first position for the first function and thereafter moved further to a second position for the second function. Such control is normally carried out by the operator, who moves the directional control valve to a first position for selecting the first function and thereafter moving the valve further to its second position for activating or accomplishing the second function.
It is desirable to free the operator of these many functions when possible. Accordingly, it is desirable to find automatic means capable of performing this function without constant attention of the operator.